The basal ganglia of the brain are involved in the initiation of movement. A major output pathway of this structure is the substantia nigra pars reticulata in the brainstem. We have studied cells in this structure, and this report describes two types of neuronal responses that are related to fixation of gaze. Cells with the first type of response decreased their discharge rate following onset of a spot of light in the visual field, but only when the monkey was not looking at another spot of light. This suppression of the visual response was not due to the act of visual fixation but rather to the presence of the visual stimulus during fixation. The point in the visual field that gave the most vigorous suppression of the high background rate was always located near the fovea. The second type of response was to the offset of the spot of light on which the monkey was fixating; the presence of any spot of light, other than the fixation light, in the visual field reduced this response. Response of these two types of cells seems to occur only at the initiation or the termination of a series of visually-guided saccades and might signal the transition between spontaneous saccades and visually-guided saccades.